None.
As is conventional, document scanners usually have a generally rectangular housing with an upper window on which a document to be scanned is placed. The housing contains a scanner carriage mounted on one or more longitudinally extending support rods or guides. The carriage is moved back and forth along the support rods by a motor driven flexible belt. Although the drive belt is slightly elastic, wear and fatigue of the belt and product dimensional variations from plastic creep phenomena and/or manufacturing tolerances gradually results in variation of the belt tension over time with resultant slippage. Accordingly, a belt tensioner mechanism is desired which is suitable for use in a document scanner so that the belt can be easily replaced when necessary by unskilled users and used to maintain proper tension throughout product life.
Various forms of belt tensioning mechanisms are well known and these generally comprise a belt tensioning pulley which is moveable from a belt installation position to a belt tensioning position in which the tensioning pulley applies the desired degree of tension to the belt under the influence of a tensioner spring. To date, belt removal or installation is difficult since the belt is easily manipulated within the close confines of a document scanner housing and screws or other fasteners should be avoided since they are easily dropped into the scanner housing to locations from which they are difficult to retrieve. Current belt tensioning systems also do not limit the travel of the belt tensioning device to protect the scanner module from catastrophic damage due to a mechanical shock induced by either customer usage or during rough handling while shipping. For purposes of the mechanical shock environment, current scanner housings utilize an additional part to function as a locking device during shipping that the customer must manually remove before using the product, leaving the scanner unprotected from mechanical shocks that can occur during customer usage or transportation. For this reason and for reasons of economy, belt tensioners have not hereto been adequate in the user handling and shipping environment. The use of a tensioner enables use of a non-stretchable belt if desired, a reduced spring tensioning force that can be utilized in a purely plastic housing structure without compromising housing integrity, and does not require a separate scanner locking device.
The present invention provides, in a document scanner which includes a housing and a belt driven moveable document scanning carriage in said housing, a belt tensioner comprising:
a) a tensioner base attached to said scanner housing for movement about a first pivot axis, said base being moveable in a plane substantially parallel to the direction of movement of said carriage;
b) a belt tensioner pulley mounted on said base for rotation about a second axis parallel to and spaced from said first axis, said pulley being engageable with a carriage drive belt; and
c) a spring affixed to said base and to said housing for biasing said base in a direction to tension said belt; said base and said housing having first engageable means for retaning said base relative to said housing in a belt installation position and second engageable means for retaining and limiting movement of said base relative to said housing in a belt tensioning position, said base being moveable with respect to said housing along said first axis to disengage said first and second engageable means to permit pivotal movement of said base relative to said housing between said positions and to a spring removal position.